Powdery mildew is an economic threat for viticulture because it not only affects grape yield, but also causes a series of impacts on the qualities of fruit and wine, especially the flavors and various metabolites. Different grape varieties may have different levels of powdery mildew resistance/tolerance and their components of their metabolome are also various. In this study, two wine grape varieties, Guipu No.6 (GP6) and Marselan (Mar) with different levels of powdery mildew tolerance, were used to compare the quality differences in metabolism level by using the widely targeted metabolomics method. The results show that GP6 has a better powdery mildew leaf tolerance than Mar. A total of 774 metabolites were detected by using a UPLC-QQQ-MS-based metabolomics approach, and 57 differential metabolites were identified as key metabolites that were accumulated after infection with powdery mildew in GP6 and Mar, including phenolic acids, flavonoids, terpenoids, stilbenes, lipids, nucleotides and derivatives, lignans and coumarins, and quinones. This finding indicates that the defense mechanisms of grape fruit are mainly associated with phenylpropane-flavonoid metabolism. Specifically, stilbenes had greater variations after powdery mildew infection in GP6; while in Mar, the variations of flavonoids, especially kaempferol-3-O-glucuronide and luteolin-7-O-glucuronide, were more remarkable. The above results demonstrate that stilbenes may play a more important role than flavonoids in resisting powdery mildew infection in GP6’s fruits, and the drastic variations of these phenolic compounds in different wine grapes after powdery mildew infection might also lead to quality difference in the flavors. This study can provide new insights into the understanding of the cause of powdery mildew tolerance in different grape varieties and the effects on the quality of wine grapes infected with the disease exerted by metabolism level.

The establishment and application of a two-crop-a-year cultivation system depends on the particularity of climatic conditions in subtropical regions. The different temperature, light, and water conditions throughout the growing season of summer and winter grapes are the fundamental reasons for differences in primary and secondary metabolites. We performed ultra-high-performance liquid chromatography–triple quadrupole mass spectrometry (UPLC-QQQ-MS)-based metabolomics on ‘Kyoho’ grapes under a two-crop-a-year cultivation system. In total, 1062 metabolites were identified and classified into 10 different categories, while flavonoids were the largest group, with 285 metabolites. Moreover, 876 metabolites were different among the four developmental stages, and 551 were different between the summer and winter grapes during the same growth period. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) clearly distinguished developmental and growth-season differences based on the detected metabolites. Of note, flavonoids were the most important compounds responsible for the differences in berry composition during the growth and developmental seasons. The content of most flavonoids was higher in the winter grapes, but some were also found at higher levels in summer grapes, such as kaempferol-4′-O-glucoside, leucocyanidin, and cyanidin-3-O-glucosylglucoside. Additionally, myricetin-3-O-arabinoside was consistently higher in winter grapes than in summer grapes during all four developmental stages. The extreme high temperature and higher relative humidity were important reasons for the lower flavonoid content in the summer grapes than in the winter grapes. Moreover, the stronger light intensity in the early development of the winter grapes had a positive effect on the accumulation of flavonoids, especially flavonols and flavan-3-ols. This study provides new insights into the metabolism of flavonoids in grapes under a two-crop-a-year cultivation system and explores the climatic causes of the differences in the metabolites in the two crops of grapes.

Grape (Vitis vinifera) is regarded as one of the most economically important fruit crops throughout the world and is widely cultivated in China. In March 2023, peduncle rot symptoms were observed on ripe grape (cv. Kyoho) of Guangxi Academy of Agricultural Sciences in Nanning, Guangxi Province (20°54' to 26°24' N, 104°26' to 112°04' E), causing severe shrink of infected grapes with incidence of 20 to 40%. Initially, a small portion of the grape peduncles turned from light brown to darker brown and gradually spread to the entire bunch of grape peduncles. Then the peduncles gradually dried up and became dark brown, resulting in necrosis and shedding of the fruits. Symptomatic peduncles were cut into small pieces (approximately 3 mm long), surface disinfected with 75% alcohol for 10 s, 1% NaOCl for 2 min followed by three washes in sterile distilled water and separately transferred to potato dextrose agar (PDA) plates. Forty-six Fusarium isolates were obtained from the seventy-five tissue pieces after 5 days of incubation at 25°C on PDA (average isolation frequency 61%). Based on the morphology, a representative isolate of Fusarium was selected for each of the three samples. Single spore isolates (PT1-1, PT3-1, and PT3-2) were selected for further study. The colonies produced abundant whitish to yellowish aerial mycelium on PDA after 7 days incubation at 25°C in the dark. Macroconidia cultured on carnation leaf agar (CLA) for 7 days were falcate, multiseptate, with a curved apical cell and foot-shaped basal cell, mostly 1-3-septate, measuring 21.3 ± 0.5 μm × 4.8 ± 0.1 μm, 24.3 ± 0.5 μm × 4.5 ± 0.1 μm, 21.9 ± 0.3 μm × 4.5 ± 0.1 μm (n=90) for PT1-1, PT3-1, and PT3-2, respectively. Microconidia were hyaline, fusoid or ovoid, 0- or 1-septate, measuring 10.5 ± 0.2 μm × 3.5 ± 0.1 μm, 10.4 ± 0.3 μm × 3.6 ± 0.1 μm, 10.0 ± 0.2 μm × 3.6 ± 0.1 μm (n=90) for PT1-1, PT3-1, and PT3-2, respectively. The internal transcribed spacer (ITS), translation elongation factor (TEF1), calmodulin (CAM) and partial RNA polymerase second largest subunit (RPB2) were amplified using primers ITS4/ITS1, EF1/EF2, CL1/CL2A, and 5F2/7cR, respectively (White et al. 1990; O'Donnell et al. 1998, 2000; Reeb et al. 2004; Liu et al. 1999). Sequences from the three isolates were deposited in GenBank (ITS: OR511756-OR511758; TEF1: OR535156-OR535158; CAM: OR535153-OR535155; RPB2: OR535159-OR535161). A maximum likelihood (ML) phylogenetic tree was constructed with RAxML version 8.2.10 based on the concatenated sequences (ITS, CAM, TEF1, RPB2). According to morphology and phylogenetic analysis, the isolates were identified as Fusarium pernambucanum (Santos et al. 2019). A pathogenicity test was performed with three isolates on twenty-four asymptomatic strings of grapes in a field in Nanning, Guangxi Province, China. On twelve strings of ripe grapes (cv. Kyoho), 3-mm-long wounds were made on the peduncle of each string of grapes with a sterile needle, followed by inoculation with conidial suspension (10⁶spores/ml in 0.1% sterile Tween 20) by misting with an atomizer until runoff (Lorenz et al. 1995). Three isolates were separately inoculated onto three strings of grapes. Controls were inoculated with water containing 0.1% sterile Tween 20 under the same conditions. The same inoculation was applied to twelve strings of non-wound grapes. Plants were covered with polythene bags to maintain high humidity for 7 days. Typical dark brown lesions were observed on all inoculated peduncles with conidia. After 14 days, the necrotic lesions spread to the entire peduncles causing them to shrivel and die. No symptoms were observed on controls. Koch's postulates were completed by reisolating the fungus from the inoculated tissues. The results of morphological identification and multigene sequence analysis obtained by reisolation were consistent with original isolates. To our knowledge, this is the first report of F. pernambucanum causing peduncle rot on grape in China. These results will provide valuable information for prevention and management of peduncle rot on grape.

The effects of different rootstocks on the grape quality and volatile aromatic compounds of ‘Shine Muscat’ were investigated. The basic physicochemical parameters of berries from five scion–rootstock combinations (SM-Beta, SM-SO4, SM-5C, SM-Fercal, SM-YN2) and own-rooted ‘Shine Muscat’ grape were measured, and their volatile aromatic compounds were determined using headspace solid-phase microextraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC-MS). Our results showed that the SM-YN2 combination exhibited the highest berry weight, and increased by 28.13% compared with SM self-rooted seedling. In addition, the ‘5C’ and ‘YN2’ rootstocks could better maintain total soluble solids (TSS), titratable acidity (TA), TSS/TA and pH in the berries, whereas the ‘Beta’, ‘SO4’ and ‘Fercal’ rootstocks impaired TSS. Volatile profiling identified 841 volatile compounds classified into 15 categories, among which terpenoids constituted the predominant contributors to berry aroma. Furthermore, 22 characteristic aroma compounds were screened, and linalool presented the highest concentration among all terpenoids in ‘Shine Muscat’ fruit. Odor activity values (OAVs) and aroma proportion analyses further revealed that linalool is the key compound for the characteristic ‘muscat’ aroma of ‘Shine Muscat’. In addition, the SM-YN2 combination exhibited 31.96% and 4.61% higher concentration and proportion of linalool compared to own-rooted vines. Notably, with the exception of ‘YN2’, ‘Beta’, ‘SO4’, ‘5C’ and ’Fercal’ downregulated the expressions of one or more terpenoid synthesis-related genes. In conclusion, grafting onto rootstock could improve berry quality, particularly the ‘YN2’ rootstock, which yielded ‘Shine Muscat’ grapes with the highest overall quality. As a resource of the East Asian grape group, ‘YN2’ can be utilized as a rootstock in future production.

Vitis heyneana Roem. et Schult. var. adenoclada (Hand.-Mazz.) is an important wild grapevine resource with unique berry traits and wine quality characteristics; yet the molecular mechanisms governing its phenolic biosynthesis remain to be further elucidated compared with cultivated Vitis vinifera. This study aimed to systematically characterize the transcriptional and metabolic regulation of phenolic compound accumulation in V. heyneana var. adenoclada using integrated metabolomics and transcriptomics. At the metabolic level, V. heyneana var. adenoclada exhibited significantly higher contents of phenolic acids (caffeic and ferulic acids), resveratrol, flavonols (quercetin and myricetin), flavan-3-ols (catechin and epicatechin), and anthocyanin diglucosides compared with V. vinifera cv. Cabernet Sauvignon. The two tested V. heyneana varieties showed distinct developmental accumulation profiles: Guiheizhenzhu No. 6 accumulated more ferulic acid, resveratrol, myricetin, and anthocyanins at maturity, whereas Yeniang No. 2 showed higher quercetin and flavan-3-ols at the green stage. Integrated multi-omics correlation analyses revealed that the elevated phenolic content is driven by the coordinated upregulation of key structural genes mediated by a complex MYB regulatory network. Specifically, MYB12 (MYBF1) positively correlated with COMT, CHI, DFR, and LAR. MYB5, MYBS3, and MYB61 promoted quercetin synthesis by activating FLS. MYB06, MYB4, and MYB36 enhanced STS transcription to drive resveratrol biosynthesis, whereas MYB1 and MYB5 cooperatively regulated UFGT, 5GT, and GST4, facilitating efficient synthesis and transport of anthocyanin diglucosides. These findings provide comprehensive mechanistic insights into phenolic metabolism in V. heyneana var. adenoclada and establish a valuable theoretical foundation for improving the flavor quality and regional utilization of wild grape wines.